Military and commercial electronic systems are often required to withstand exposure to extremely high levels of electromagnetic interference (EMI) and radio frequency (RF) electromagnetic (EM) field levels. Field strengths can exceed 27,000 volts/meter in specific portions of a broader frequency range of 0.01 MHz to 50 GHz (see MIL-STD-464C). Electronic systems must be hardened to withstand exposure to such high-level EMI and EM fields. These requirements apply both when a system is operational (i.e., fully powered and activated) and when a system is non-operational (i.e., deactivated and powered “OFF”).
High field strength waves captured by the antenna of radar or wireless communications equipment may induce RF signal levels in the system electronics that greatly exceed the damage threshold of electronic components within the system. Depending upon the specific system, RF levels within the electronics may approach or exceed hundreds or thousands of watts. These electronic systems are susceptible whether powered-on or powered-off. Since antennas and antenna connections for these systems are passive, no special protection is provided when unpowered or deactivated.
Modern practical radar and wireless communications systems depend upon receiver electronics capable of detecting and decoding weak RF signals. Components for such receivers use small semiconductor geometries to effectively amplify weak RF signals to acceptable levels for detection and decoding. The sizes of these semiconductor features are further reduced in receiver components to minimize costs and maximize efficiencies. Damage or destruction to these small semiconductor features will occur when exposed to high RF or EMI levels due to thermal stresses or electrical breakdown. Similar damage may occur to RF control and routing components placed between the system antenna and receiver and to system transmitter components. As a consequence, radar and wireless systems are vulnerable to high field strength EMI and RF events.
Therefore, there is a need for improved circuitry for suppression of high-power electromagnetic interference (EMI) signals. In particular, there is a need for radio frequency (RF) protection circuitry that protects radars and similar systems from high field strength EMI exposure both in the powered “ON” or active state and in the unpowered or “OFF” state.